Rack mountable servers are generally shaped and sized based on industry standards. For example, a standard server-rack configuration, one rack unit or 1 U is 19 inches (480 mm) wide and 1.75 inches (44 mm) tall. The most common computer rack form-factor is 42 U high, which can receive up to 42 discrete computer devices that are directly mountable in the rack.
To maximize storage capacity of certain servers, rack mountable or otherwise, disk drives are tightly packed side by side within an enclosure. A 1 U server hosting either eight (8λ) or twelve (12λ) disk drives is an example of a densely packed storage server. Such a server has very little space for air movement between each disk drive. Thus, it will be understood that placing a large number of disk drives close together can introduce cooling issues.